linux-kernel - Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation

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Date:   Tue, 23 Apr 2019 09:33:53 -0500
From:   Alex G <mr.nuke.me@...il.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     bhelgaas@...gle.com, helgaas@...nel.org, linux-pci@...r.kernel.org,
        austin_bolen@...l.com, alex_gagniuc@...lteam.com,
        keith.busch@...el.com, Shyam_Iyer@...l.com, lukas@...ner.de,
        okaya@...nel.org, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/LINK: Account for BW notification in vector
 calculation

On 4/22/19 7:33 PM, Alex Williamson wrote:
> On Mon, 22 Apr 2019 19:05:57 -0500
> Alex G <mr.nuke.me@...il.com> wrote:
>> echo 0000:07:00.0:pcie010 |
>> sudo tee /sys/bus/pci_express/drivers/pcie_bw_notification/unbind
> 
> That's a bad solution for users, this is meaningless tracking of a
> device whose driver is actively managing the link bandwidth for power
> purposes. 

0.5W savings on a 100+W GPU? I agree it's meaningless.

> There is nothing wrong happening here that needs to fill
> logs.  I thought maybe if I enabled notification of autonomous
> bandwidth changes that it might categorize these as something we could
> ignore, but it doesn't.
> How can we identify only cases where this is
> an erroneous/noteworthy situation?  Thanks,

You don't. Ethernet doesn't. USB doesn't. This logging behavior is 
consistent with every other subsystem that deals with multi-speed links. 
I realize some people are very resistant to change (and use very ancient 
kernels). I do not, however, agree that this is a sufficient argument to 
dis-unify behavior.

Alex